Abstract
The charge-state dependence of the binary-encounter-electron (BEE) double-differential cross section (DDCS) at 0° with respect to the beam direction resulting from collisions of 1 MeV/amu , , , , , , and , and 0.5 MeV/amu with is reported. The data show an enhancement in the BEE DDCS as the charge state of the projectile is decreased, in agreement with the data reported by Richard et al. [J. Phys. B 23, L213 (1990)]. The DDCS enhancement ratios observed for the three-electron isoelectronic sequence :, :, :, and : are about 1.35, whereas a DDCS enhancement of 3.5 was observed for . The BEE enhancement with increasing electrons on the projectile has been shown by several authors to be due to the non-Coulomb static potential of the projectile and additionally to the e-e exchange interaction. An impulse-approximation (IA) model fits the shape of the BEE DDCS and predicts a dependence for the bare-ion cross sections. The IA also predicts a binary peak energy that is independent of q and and below the classical value of 4t, where t is the energy of electrons traveling with the projectile velocity. We observed a BEE energy shift ΔE (ΔE=4t-, where is the measured energy at the peak of the binary encounter electrons) that is approximately independent of q for the low- ions, whereas the measured ΔE values for Si, Cl, and Cu were found to be q dependent.
- Received 15 July 1993
DOI:https://doi.org/10.1103/PhysRevA.48.4421
©1993 American Physical Society